1. Field of the Invention
The present invention provides cement compositions and methods of cementing within subterranean formations penetrated by well bores wherein the flow properties of one or more dry particulate cementitious materials used therein are improved and wherein the materials can be readily conveyed out of storage tanks and the like.
2. Description of the Prior Art
Cementitious materials are commonly utilized in subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipes such as casings and liners are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of the well bore and the exterior surfaces of pipe disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe in the well bore and bonds the exterior surfaces of the pipe to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
Cementitious materials such as hydraulic cements, slag, fumed silica, fly ash and the like having various particle size distributions are often dry-blended and placed in storage tanks. The storage tanks containing the cementitious materials are also often transported by land or sea to locations where the cementitious materials are to be used. During such transportation, the cementitious materials are subjected to vibrations and as a result, the materials are tightly packed under static conditions. One or more of the cementitious materials are often of ultra-fine particle sizes, i.e., sizes in the range of from about 5 to about 100 microns, which causes the tightly packed problem to be more severe. When the cementitious materials are conveyed out of the storage tanks at the locations of use, significant portions of the tightly packed materials are often left in the storage tanks. The incomplete conveying of the materials results in costs for disposing of the materials and increased costs to the person or entity using the cementitious materials.
Cementitious materials have heretofore been treated to make them more flowable. For example, U.S. Pat. No. 2,857,286 issued to Striker on Oct. 21, 1958 discloses a process of treating Portland cement with acetic acid or a water soluble salt of acetic acid whereby the Portland cement becomes more flowable. In accordance with the Striker patent, the treatment of Portland cement with the acid or acetate is carried out either concurrently with, or subsequent to, the grinding of the cement clinker. The acid or acetate can be combined with the cement during grinding or the ground cement can be treated by injecting the acid or acetate into the cement under pressure as a vapor in order to blow the cement and uniformly contact it with the acid or acetate.
U.S. Pat. No. 3,094,425 issued to Adams et al. on Jun. 18, 1963 discloses that most cements compacted by vibration become semi-rigid and will not flow without considerable mechanical effort to break up the compaction. This condition is known as "pack set." Further, it is stated that it is known that certain polar molecules when added to ground cement will attach to the cement particles and reduce their surface forces. In accordance with the Adams patent, a mixture of calcium acetate and lignin sulfonate is an effective grinding aid and a pack set inhibitor when added to the cement mill and interground with the cement.
U.S. Pat. No. 3,615,785 issued to Moorer et al. on Feb. 2, 1968 discloses a cement grinding aid and pack set inhibitor comprised of polyol and a water soluble salt of an aliphatic acid having no more than 3 carbon atoms.
The above described additives are difficult to handle and must be added to the cement prior to or after grinding. Since commercially available cementitious materials generally do not include such additives, they must be provided, handled and combined with ground cement by the user by spraying, mechanical mixing or other time consuming procedure.
Thus, there are continuing needs for improving the flow properties of dry particulate cementitious materials used in cement compositions for cementing in subterranean formations penetrated by well bores wherein the materials can be readily conveyed out of storage tanks and the like.